Optical switches and other optoelectronic devices have advanced rapidly with developments in manufacturing technologies over the years. With the advent of Micro Electro Mechanical Systems (MEMS) technology, such devices could be made smaller, but problems arose when trying to align a light beam emitting from an optical fiber transporting light between a light source and transmission/conversion chips. These conversion chips generally provide the function of optical switching or conversion to/from electrical signals. For single-mode optical fibers, the tolerance of alignment between fibers and the targeted area is usually about 0.1 xcexcm. Multi-mode optical fibers have a slightly wider alignment tolerance, however this is usually still below 5 xcexcm. Such high-precision alignments are currently performed manually and are expensive.
An additional disadvantage of current Micro Optical Electrical Mechanical Systems (MOEMS) is that in order to tolerate misalignment of optical fibers, the active area of the photodiode is generally enlarged to cover all areas on which light can project. A larger active area yields a larger p-n junction, resulting in a large junction capacitance that can lower the switching speed of the MOEMS system. Manual alignment is generally needed in the aforementioned system to achieve higher conversion efficiency.
For these reasons, development of a low cost, high-precision alignment mechanism for fiber-chip connections is important to, for example, reduce the cost of hardware of optical fiber communication systems and also reduce the costs of many optical systems that require optical fibers as media for guiding light signals.
The principles of the present invention provide for a Micro Optical Electro Mechanical System (MOEMS) including a MEMS mirror module for high-precision alignment between optical fibers and MOEMS chips. Instead of aligning chips and optical fibers under a microscope, the present invention uses an easier method: adjusting the path of a light beam emerging from an optical fiber with MEMS mirrors such that the light beam projects on a targeted area. The beam divergence problem introduced when the light waves travel through free space between mirrors can be solved by passing the beam through a curved optical element, such as a spherically curved mirror or a lens in the mirror module, to converge and/or collimate the light. Through experiments, it was found that the efficiency of, for example, a five-mirror module is on the order of approximately 62.4% when the MEMS mirrors are coated with gold, which is high enough for most applications.